"If we want to bring about real change, then the choice isn’t between protest and politics. We have to do both," wrote the former president.
Trump's remarks follow a weekend of nationwide protests over police brutality and racial injustice.
The flag symbolizes the death of the United States, the new ad from The Lincoln Project notes.
Meanwhile, at least 15 states have seen an uptick in new COVID-19 cases.
"No quarter for insurrectionists, anarchists, rioters, and looters,” the Arkansas Republican senator tweeted.
Bystander video shows the Fort Lauderdale officer pushing the protester, whose hands were in the air.
An officer in Seattle appeared to use the dangerous technique twice in a scene that was caught on video.
Rep. Joyce Beatty said she attended Columbus protests demanding justice for George Floyd "in solidarity" with demonstrators.